The present invention relates generally to the continuous separation of solid particles from a liquid by the use of a centrifugal field. More particularly the present invention relates to the use of a cone (disc) stack centrifuge configuration within a self-driven centrifuge in order to achieve enhanced separation efficiency.
Diesel engines are designed with relatively sophisticated air and fuel filters (cleaners) in an effort to keep dirt and debris out of the engine. Even with these air and fuel cleaners, dirt and debris will find a way into the lubricating oil of the engine. The result is wear on critical engine components and if this condition is left unsolved or not remedied, engine failure. For this reason, many engines are designed with full flow oil filters that continually clean the oil as it circulates between the lubricant sump and engine parts.
There are a number of design constraints and considerations for such full flow filters and typically these constraints mean that such filters can only remove those dirt particles that are in the range of 10 microns or larger. While removal of particles of this size may prevent a catastrophic failure, harmful wear will still be caused by smaller particles of dirt that get into and remain in the oil. In order to try and address the concern over smaller particles, designers have gone to bypass filtering systems which filter a predetermined percentage of the total oil flow. The combination of a full flow filter in conjunction with a bypass filter reduces engine wear to an acceptable level, but not to the desired level. Since bypass filters may be able to trap particles less than approximately 10 microns, the combination of a full flow filter and bypass filter offers a substantial improvement over the use of only a full flow filter.
The desire to remove these smaller particles of dirt has resulted in the design of high speed centrifuge cleaners. One product which is representative of this design evolution is the SPINNER II.RTM. oil cleaning centrifuge made by Glacier Metal Company Ltd., of Somerset, Ilminister, United Kingdom, and offered by T. F. Hudgins, Incorporated, of Houston, Tex. The following description of the SPINNER II.RTM. product is taken directly from a product brochure copyrighted in 1985 and published by T. F. Hudgins, Incorporated:
Now there is SPINNER II.RTM.. It is a true high-speed centrifuge that removes dense, hard, abrasive particles as tiny as 0.1 micron. That's 400 times smaller than the dirt removed by your full-flow filter. And because the SPINNER II.RTM. is a real centrifuge that slings dirt out of the path of circulating oil, it maintains a constant flow throughout its operating cycle. In fact, tests show that the SPINNER II.RTM. unit is so good, it reduces engine wear half-again as much as even the best full-flow/bypass filter combination. PA1 Best of all, the SPINNER II.RTM. oil cleaning centrifuge is low-cost because it is powered only by the engine's own oil pressure: less than five percent of the cost of-the traditional electric-motor-driven centrifuge. Now you can install the most cost-effective oil cleaning system with the best wear reduction available today--on all your industrial engines. PA1 The SPINNER II.RTM. oil cleaning centrifuge consists of three sections--the centrifuge bowl, the driving turbine and the oil--level control mechanism--all contained in a rugged steel and cast aluminum housing. PA1 To get to the centrifuge, dirty oil from the engine enters the side of the SPINNER II.RTM. housing and travels up through the hollow spindle. At the top of the spindle, a baffle distributes the oil uniformly into the centrifuge bowl. Because the bowl spins at about 7500 rpm, the oil quickly accelerates to a high speed. The resulting centrifugal force slings dirt outwardly onto the bowl wall where it mats into a dense cake. PA1 Clean oil leaves the bowl through the screen and enters the turbine section. Here the engine's oil pressure expels the oil through two jets that spin the turbine and attached centrifuge bowl. Oil pressure alone drives this highly efficient unit.
The construction and operating theory of the SPINNER II.RTM. oil cleaning centrifuge is described in the foregoing publication in the following manner:
While the SPINNER II.RTM. might seem to be the complete answer to the task of effective oil filtration and cleaning, there are other high-speed centrifuge designs. There are also design shortcomings with the SPINNER II.RTM. from the standpoint of filtering or cleaning efficiency. First, with regard to other high-speed centrifuge designs, the SPINNER II.RTM. literature makes reference to other high-speed, electric-motor-driven centrifuges, such as those made by Alfa Laval, Bird, and Westphalia. As stated by the SPINNER II.RTM. literature, these motor-driven centrifuges are "too expensive (upwards of $10,000) and too complex for general use".
With regard to the aforementioned design inefficiencies of the SPINNER II.RTM., FIG. 1 represents a diagrammatic, cross-sectional view of the type of self-driven centrifuge which is similar to or representative of the SPINNER II.RTM. design. All components shown in the FIG. 1 drawing rotate upon a shaft which provides pressurized oil to the inlet ports of the centertube. After passing through the two inlet ports of the rotating spindle or tube, the oil is directed towards the top of the shell (bowl) by the top baffle. The oil then spills over the baffle and short circuits directly toward the outlet screen, leaving a majority of the centrifuge body in a completely stagnant condition. This result is unfortunate because the centrifugal force increases proportionately with distance from the axis and in this design, the flow stays very close to the axis. After passing the outlet screen, the oil passes underneath the bottom baffle plate and exits through two tangential directed nozzles which also serve to limit the oil flow rate through the centrifuge. The high velocity jets exiting the two nozzles generate the reaction torque needed to drive the centrifuge at sufficiently high rotation speeds for particle separation (3000-6000 rpm).
As stated in the SPINNER II.RTM. product literature, there are other high speed centrifuges, including electric-motor-driven designs such as those made by Alfa Laval. Besides being motor-driven, the Alfa Laval design is appropriate to consider relative to the present invention for its use of a disc-stack assembly. The disc inserts which comprise the heart of the disc-stack assembly enable the sedimentation height to be reduced, thereby resulting in greater filtering efficiency. The disc inserts are conical in shape and are assembled with circular or long rectangular plates known as caulks which are fitted between adjacent disc inserts. Separation channels are formed as a result and the thickness of the caulks may be varied so as to adjust the height of the separation channel for the particular particle size and concentration. The theory of operation and structure of the Alfa Laval disc stack separators are described in the Alfa Laval product literature and are believed to be well known to those of ordinary skill in the art. One such Alfa Laval publication is entitled "Theory of Separation" and was published by Alfa Laval Separation AB of Tumba, Sweden. Another publication with a similar disclosure or teaching was an article entitled "New Directions in Centrifuging" which was published in the January, 1994 issue of Chemical Engineering, pages 70-76, authored by Theodore De Loggio and Alan Letki of Alfa Laval Separation Inc.
The flow of liquid through some of the Alfa Laval disc-stack separator arrangements begins with the liquid entering at the top and flowing to the bottom where it is radially diverted and flows upwardly toward the fluid exit locations. The upward flowing liquid enters each separation channel at its outer radius edge and flows upwardly and radially inward through the channel to its point of exit at the inner radius edge. Separation of solid particles takes place as the liquid flows through the separation channels. In other Alfa Laval arrangements the flow through the disc-stack begins at an upper edge. However, in both styles the fluid exit location is at the top of the assembly.
After considering the design features and performance aspects of the centrifuge arrangements which are generally depicted by the aforementioned SPINNER II.RTM. and Alfa Laval structures, the inventors of the present invention conceived of an improved design for a bypass circuit centrifuge. Involved in the design effort by the present inventors was the use of computational fluid dynamics analysis of self-driven engine lube system centrifuges and this analysis revealed sub-optimal flow conditions from a particle separation standpoint. Additional research revealed that a greater degree of separation efficiency in a centrifuge could be achieved by using a stack of cones so as to reduce the necessary particle settling distance. However, the Alfa Laval centrifuge requires a motor-drive arrangement which represents a significant drawback from the standpoint of size, weight and cost.
What the present invention achieves is a combination of the low cost self-driven type centrifuge similar in some respects to the SPINNER II.RTM. but with the efficiency enhancement provided by a unique arrangement of stacked cones. The result is a cost effective, higher performance centrifuge which can be used to replace engine mounted disposable bypass filters. Although it was initially theorized that the self-driven centrifuge concept would not provide sufficient power to drive the stacked cone type of centrifuge, specific provisions have been made by the present invention to enable that combination in a unique and unobvious way. As conceived, the improved design of the present invention captures the lower cost benefits of the self-driven centrifuge with the greater efficiency of the disc-stack of cones. Due to the specific flow directions of the oil through the SPINNER II.RTM. and through the disc-stack configuration of the described Alfa Laval concept, a direct combination of these two designs was not possible. Specific and unique components had to be created in order to make the flow directions compatible and in order to enable a disc-stack of cones to be integrated into a self-driven bypass circuit centrifuge. According to the preferred embodiment of the present invention, a bypass circuit centrifuge is provided for maintaining cleanliness of an engine lubricant sump. The centrifuge is self-driven with system oil pressure by means of tangential nozzles and further contains a stack of closely spaced parallel truncated cones in order to increase separation efficiency. The present invention has a broader range of application than merely engine lubricants. The disclosed centrifuge can be used for a variety of fluids whenever it is desired to separate particulate matter out of a circulating flow, assuming that the necessary fluid pressure is present to drive the centrifuge.
In addition to the product literature already mentioned, there are a number of patents which disclose various filtering and centrifuge designs and advance a variety of theories as to the specific and preferred operation. The following patent references are believed to provide a representative sampling of such earlier designs and theories.
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